Expanding the tagging toolbox for visualizing translation live.

Translation is a highly regulated process that includes three steps: initiation, elongation, and termination. Tremendous efforts have been spent to study the regulation of each translation step. In the last two decades, researchers have begun to investigate translation by tracking it in its native and live intracellular environment with high spatiotemporal resolution. To achieve this goal, a handful of tagging tools have been developed that can distinguish nascent chains from previously synthesized mature proteins. In this review, we will focus on these tagging tools and describe their development, working mechanisms, and advantages and drawbacks in tracking translation in live mammalian cells and organisms. In the second part of the review, we will summarize novel discoveries in translation by a recently developed nascent polypeptide tracking technology using tandem epitope tag array tagging tools. The superior spatiotemporal resolution of this technology enables us to directly and continuously track nascent chains live and thus reveal preferred translation location and timing, as well as the kinetics of canonical and noncanonical translation, translation bursts, ribosome quality control, and nonsense-mediated mRNA decay. In the future, we expect more tagging tools to be developed that allow us to track other regulation processes of a protein, such as folding, modifications, and degradation. With the expanding tagging toolbox, there is potential that we can track a protein from translation to degradation to fully understand its regulation in a native live cell environment.